[Wiener spectrum and relative electron density resolution in heavy ion CT based on measurement of residual range distribution].

The relative electron density resolution was discussed by the Wiener spectrum in the heavy ion CT image. The two-dimensional (2D) Wiener spectrum in the CT image was obtained from the one-dimensional (1D) Wiener spectrum of the measured residual range distribution of the water phantom for a single projection angle, and the relative electron density resolution in the CT image was calculated from the 2D Wiener spectrum. To examine the usefulness of this method, the relative electron density resolution was also estimated by other two methods; the calculation using the Wiener spectrum of the reconstructed image of the water phantom, and the estimation by the reconstructed image of the electron density resolution phantom. The result of the first method was similar to those of the other two methods. Therefore, it is useful to estimate the relative electron density resolution by the 1D Wiener spectrum of the measured residual range distribution of the water phantom for a single projection angle.

Heavy ion CT system based on measurement of residual range distribution.

The heavy ion CT system is proposed which is based on measurement of the residual range distribution by a fluoroscopy detector consisting of an intensifying screen and a CCD video camera. To investigate the fundamental performance of the proposed system, the spatial and density resolutions of the CT image were evaluated. The heavy ion beam 12C accelerated up to 400 MeV/u by HIMAC was used in this study. A series of projection images of two types of phantoms (PMMA pipes with several sizes and various kinds of rods with different electron densities) were experimentally taken for five values of range shifter thickness at each projection angle. From these images, the residual range distribution was obtained and used to reconstruct CT images of the relative stopping power which were obtained by the filtered back projection method with the Shepp-Logan filter after noise reduction processing by the median filter. As a result, the spatial resolution was found to be less than 2 mm and the relative density resolution around the density of water was less than 0.07.